Self-centering (SC) rocking earthquake lateral force resisting systems (LFRS) include post-tensioned walls and post-tensioned concentrically-braced frames. Research by various groups in the US, New Zealand, Canada, Japan, and Europe has shown that, unlike a conventional LFRS, these self-centering LFRS can be designed to suffer only modest damage from the design basis earthquake (DBE), owing to the use of a joint-gap-opening deformation mechanism rather than the inelastic member deformation mechanism used in a conventional LFRS. Research on post-tensioned SC rocking concentrically-braced frame (SC-CBF) systems at Lehigh University showed that these LFRS could be designed to be essentially without structural damage (i.e., “damage-free”) under the DBE, enabling a SC-CBF building to be functional after the DBE. The presentation will include results from hybrid earthquake simulations on a large-scale SC-CBF laboratory specimen, as well as numerical simulations.

For the SC-CBF system, it was found that damage states for the post-tensioning steel are closely-related to the first-mode deformation response, while damage states for the members of the concentrically-braced frame are closely-related to the higher-mode force response. To achieve damage-free performance under the DBE, engineering of SC-CBF system (and other SC rocking LFRS) must account for the higher-mode response. Several approaches are considered: (1) design for extreme value higher-mode forces to avoid inelastic member response under the DBE; (2) use of a second rocking mechanism within the concentrically-braced frame to control second-mode response; and (3) use of deformable connections between the floor system and LFRS to control the forces transmitted to the LFRS. The presentation will discuss an approach for quantifying the higher-mode response, denoted as the effective pseudo-acceleration. Using the effective pseudo-acceleration, extreme value higher-mode responses are quantified for use in design of SC-CBFs. In addition, using the effective pseudo-acceleration, an approach for designing a second rocking mechanism to control the second-mode response is summarized. Finally, an alternative approach for controlling the higher mode response, using deformable connections between the floor system and LFRS, is summarized.

Biography:

Richard Sause is Joseph T. Stuart Professor of Structural Engineering and Director of the Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center at Lehigh University. His research interests include self-centering earthquake-resistant systems; seismic performance of precast concrete, reinforced concrete, and steel structures; and seismic performance of structures with supplemental dampers. His research contributions and collaborations have been recognized with several US national awards, including the Charles Pankow Award for Innovation (ASCE, 2016), the Leslie D. Martin Award for Merit (PCI, 2014); the Raymond C. Reese Research Prize (ASCE, 2009); the J. James R. Croes Medal (ASCE, 2007); the Charles C. Zollman Award (PCI, 2006); and the Raymond C. Reese Structural Research Award (ACI, 1987).

The New Zealand Society for Earthquake Engineering Inc.

A collaborating technical group of the Institution of Professional Engineers New Zealand